downgrading drivers completely remove this crash BUT brings back the lag.

ALSO some very basic 2D apps start playing up:
gvim.
When executed under the 260.x drivers and using openbox as the desktop environment the GUI is non-responsive.
IF gvim is launched: gvim -f it is usable but the save/open gtk dialog is non-functional.

I upgraded to 260.19.12 today in hopes of getting rid of video tearing (from both vdpau and non-vdpau apps) and ran smack dab into the gvim problem. Gvim -f is often usable but I have a lot of breakage because I call gvim from about a dozen scripts, none of which use the -f flag.